Right now you’re functioning on one hour’s sleep a night (something perhaps only a 17-year-old could do), your bedroom is a makeshift office with a desk squeezed between the bed and the wall and mum is on your case about knuckling down with school work so you can apply to university. But already the money’s coming in, so you know you’re on to something good.

In the next few months, while your school friends are writing personal statements, know that you’ll never regret your decision to skip academia and lead an entrepreneurial life. Don’t be alarmed when your instant reaction to mum’s coaxing is: “That’s never going to happen – I’m already doing exactly what I want to do.”

If I could just say one thing: I envy you. At 17, I was never afraid to follow my gut and rip up the rule book, because I had no idea what the rule book was. That’s why you’ll find yourself risking every penny you have made so far on taking out ad space in a magazine (a risk that pays off, by the way).

Barnaby aged 17. Photograph: PR

That’s also why you will have the guts to pick up the phone and call a competitor to ask him: “Why do you charge so much for something that’s so cheap to provide?” When he replies: “Because that’s what everyone has always done”, you, as a naive newcomer, will not think twice about slashing your prices by 50%. A move that will allow you to hire six employees, grow to 24,000 customers, and why several competitors will want to buy your business.

Your innocence is your biggest asset. But there are a few tips I can give you for when you think it’s not:

1. In the first few years, you’ll have to learn how people think, and consider what they want and need from your service. You’ll also have to devote time to proving yourself and earning respect, and it must be earned.

2. It will take years for the business to build a reputation and there is no way to rush that or do it faster.

3. Let go of the reins on customer support as quickly as you can. You’re not very good at it, and you can’t take criticism from customers very well. You’ll fix this by enabling others, who know better, to do it for you.

4. Seek out wisdom from older, wiser business owners, extend your peer network, and employ people who are better than you and can do the many things you cannot. There’s no room for arrogance or pride when it comes to operational success.

5. Be a proud penny pincher. Don’t rent office space until you’ve entirely outgrown your bedroom, and then your kitchen table, and if you outsource instead of hiring permanent staff, you’ll be able to work from home a while longer. It might be lonely, but it’s also saving you thousands of pounds a month.

6. As the business grows, you’ll find it dangerously easy to become a manager and stop being a leader. A never-ending torrent of demands from staff and customers is inevitable, but you don’t have to deal with all this yourself. The minute you reach that tipping point where you’re so bogged down in managing that you cannot progress the business to the next stage, you need to hire.

7. Persistence pays. When you’re young, sticking at things doesn’t come naturally. But that willingness to slog it out through the many very difficult times (like the time we had a major outage and I had to make the two-and-a-half hour trip between Birmingham and London four times in 48 hours with no sleep) will give you the edge.

But more than anything, I want to tell you to think about your approach to business right now, and carry it with you throughout your entire career. When you’re a bit older and, incidentally, running business number two, your innocence and naivety will slowly disappear.

You’ll be working seven day weeks and ​will be desperately unhappy

You will try to follow the rule book, and you’ll forget how you once took risks. You’ll have 35 employees and the pressure of that responsibility will stymie your creativity and potential for innovation. You’ll be working seven day weeks, stuck in endless, pointless meetings, and will be desperately unhappy.

It’s at that point that you’ll snap, rip up the rule book once again, and create something fantastic and refreshingly disruptive. So be brave, don’t be afraid to make bold decisions, and try never, ever to lose the 17-year-old inside.

Barnaby, aged 34

Barnaby Lashbrooke is founder of Time Etc

Are you an entrepreneur who would like to write a letter to your younger self? Email us at smallbusinessnetwork@theguardian.com to take part in this series.

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